Add support for sysroots to GN's pkg-config.

build/config/linux/pkg-config.py

Index: build/config/linux/pkg-config.py
diff --git a/build/config/linux/pkg-config.py b/build/config/linux/pkg-config.py
index 40988d9792eada3a99ce7569fd67df8990edd388..6248dafb707ac845f8d459bf6e41a3980ed2ab90 100644
--- a/build/config/linux/pkg-config.py
+++ b/build/config/linux/pkg-config.py
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import json
+import os
 import subprocess
 import sys
 import re
@@ -17,6 +18,13 @@ from optparse import OptionParser
 # You can filter out matches using "-v <regexp>" where all results from
 # pkgconfig matching the given regular expression will be ignored. You can
 # specify more than one regular expression my specifying "-v" more than once.
+#
+# You can specify a sysroot using "-s <sysroot>" where sysroot is the absolute
+# system path to the sysroot used for compiling. This script will attempt to
+# generate correct paths for the sysroot.
+#
+# When using a sysroot, you must also specify the architecture via
+# "-a <arch>" where arch is either "x86" or "x64".
 
 # If this is run on non-Linux platforms, just return nothing and indicate
 # success. This allows us to "kind of emulate" a Linux build from other
@@ -25,8 +33,77 @@ if sys.platform.find("linux") == -1:
   print "[[],[],[]]"
   sys.exit(0)
 
+
+def SetConfigPath(options):
+  """Set the PKG_CONFIG_PATH environment variable.
+  This takes into account any sysroot and architecture specification from the
+  options on the given command line."""
+
+  sysroot = options.sysroot
+  if not sysroot:
+    sysroot = ""
+
+  # Compute the library path name based on the architecture.
+  arch = options.arch
+  if sysroot and not arch:
+    print "You must specify an architecture via -a if using a sysroot."
+    sys.exit(1)
+  if arch == 'x64':
+    libpath = 'lib64'
+  else:
+    libpath = 'lib'
+
+  # Add the sysroot path to the environment's PKG_CONFIG_PATH
+  config_path = sysroot + '/usr/' + libpath + '/pkgconfig'
+  config_path = ':' + sysroot + '/usr/share/pkgconfig'
+  if 'PKG_CONFIG_PATH' in os.environ:
+    os.environ['PKG_CONFIG_PATH'] += ':' + config_path
+  else:
+    os.environ['PKG_CONFIG_PATH'] = config_path
+
+
+def GetPkgConfigPrefixToStrip(args):
+  """Returns the prefix from pkg-config where packages are installed.
+  This returned prefix is the one that should be stripped from the beginning of
+  directory names to take into account sysroots."""
+  # Some sysroots, like the Chromium OS ones, may generate paths that are not
+  # relative to the sysroot. For example,
+  # /path/to/chroot/build/x86-generic/usr/lib/pkgconfig/pkg.pc may have all
+  # paths relative to /path/to/chroot (i.e. prefix=/build/x86-generic/usr)
+  # instead of relative to /path/to/chroot/build/x86-generic (i.e prefix=/usr).
+  # To support this correctly, it's necessary to extract the prefix to strip
+  # from pkg-config's |prefix| variable.
+  prefix = subprocess.check_output(["pkg-config", "--variable=prefix"] + args,
+      env=os.environ)
+  if prefix[-4] == '/usr':
+    return prefix[4:]
+  return prefix
+
+
+def MatchesAnyRegexp(flag, list_of_regexps):
+  """Returns true if the first argument matches any regular expression in the
+  given list."""
+  for regexp in list_of_regexps:
+    if regexp.search(flag) != None:
+      return True
+  return False
+
+
+def RewritePath(path, strip_prefix, sysroot):
+  """Rewrites a path by stripping the prefix and prepending the sysroot."""
+  if os.path.isabs(path) and not path.startswith(sysroot):
+    if path.startswith(strip_prefix):
+      path = path[len(strip_prefix):]
+    path = path.lstrip('/')
+    return os.path.join(sysroot, path)
+  else:
+    return path
+
+
 parser = OptionParser()
 parser.add_option('-v', action='append', dest='strip_out', type='string')
+parser.add_option('-s', action='store', dest='sysroot', type='string')
+parser.add_option('-a', action='store', dest='arch', type='string')
 (options, args) = parser.parse_args()
 
 # Make a list of regular expressions to strip out.
@@ -35,9 +112,15 @@ if options.strip_out != None:
   for regexp in options.strip_out:
     strip_out.append(re.compile(regexp))
 
+SetConfigPath(options)
+if options.sysroot:
+  prefix = GetPkgConfigPrefixToStrip(args)
+else:
+  prefix = ''
+
 try:
   flag_string = subprocess.check_output(["pkg-config", "--cflags", "--libs"] +
-      args)
+      args, env=os.environ)
   # For now just split on spaces to get the args out. This will break if
   # pkgconfig returns quoted things with spaces in them, but that doesn't seem
   # to happen in practice.
@@ -46,27 +129,26 @@ except:
   print "Could not run pkg-config."
   sys.exit(1)
 
+
+sysroot = options.sysroot
+if not sysroot:
+  sysroot = ''
+
 includes = []
 cflags = []
 libs = []
 lib_dirs = []
 
-def MatchesAnyRegexp(flag, list_of_regexps):
-  for regexp in list_of_regexps:
-    if regexp.search(flag) != None:
-      return True
-  return False
-
 for flag in all_flags[:]:
   if len(flag) == 0 or MatchesAnyRegexp(flag, strip_out):
     continue;
 
   if flag[:2] == '-l':
-    libs.append(flag[2:])
+    libs.append(RewritePath(flag[2:], prefix, sysroot))
   if flag[:2] == '-L':
-    lib_dirs.append(flag[2:])
+    lib_dirs.append(RewritePath(flag[2:], prefix, sysroot))
   elif flag[:2] == '-I':
-    includes.append(flag[2:])
+    includes.append(RewritePath(flag[2:], prefix, sysroot))
   else:
     cflags.append(flag)